Traveling wave electronic tube



March 3, 1953 J. w. TILEY 2,630,544

TRAVgiLING WAVE ELECTRONIC TUBE Filed March 20. 1948 2 SI-IEETSS}EET 1 INI/ENTOR. JUH/V W 71115]! ATTORNEY March 3, 1953 Filed March 20. 1948 J. w. TILEY 2,630,544

TRAVELING WAVE ELECTRONIC TUBE 2 Sl-IEETSSHEET 2 Ja l/V W TILES agg- Patented Mar. 3, 1953 TRAVELING WAVE ELECTRONIC TUBE John W. Tiley, Philadelphia, Pa., assignor to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application March 20, 1948, Serial No. 16,011

13 Claims. 1

The present invention relates generally to the electromagnetic traveling wave tube art, and more particularly to novel apparatus based upon the principles of beam traveling wave electron tubes and adapted to produce high intensity, high velocity beams of charged particles.

This application is a continuation-in-part of my co-pending patent application Serial No. 761,798, filed July 18, 1947, which issued as Patent No. 2,541,843 on February 13, 1951. For information purposes, reference is made to my copending patent applications Serial No. 788,724, filed November 28, 1947, and Serial No. 4,849,filed January 28, 1948, which issued as Patent No. 2,584,308 on February 5, 1952. The latter two applications are also continuations-in-part of the aforesaid parent application Serial No. 761,798.

Beams of high velocity, high energy electrostatically charged particles have extensive application in the physical arts. The conventional type cathode ray tube is an example of a common use of a high energy electron beam. For use in connection with nuclear studies, special beam generating apparatus has been developed, including such particle generators as the cyclotron and the synchrotron.

It is well known in the art that a charged particle, such as the electron, may be accelerated to an extremely high velocity and consequently high energy level by allowing the electron freely to traverse a path within a high voltage electric field. For particle velocities approximately one tenth that of the velocity of light or less, the final velocity of the electron is proportional to the square root of the accelerating potential. It has been generally recognized that the generation of particle beams solely through the use of high potential accelerating fields is impractical when it is desired to obtain extremely high energy particles. The application of a potential between 50,000 volts and 1,000,000 volts involves numerous special electrical design considerations and presents a distinct hazard to operating personnel. Extremely high voltage cathode ray tubes, as required for large television images of considerable brightness, are particularly hazardous since these high voltages must be present in the home, where serious harm may be caused by failure to incorporate reliable safety apparatus.

Modern particle accelerators such as the cyclotron and others obtain high energy particles by imparting to these particles a considerable number of cumulative accelerating impulses, and thereby successively raise the total particle energy to the desired level. However, a cyclotron or like machine is wholly impractical outside the laboratory, principally because of its huge size and cost.

A recent electronic development, known as the beam traveling wave tube is utilized, in accordance with the principles of the present invention, to provide means for obtaining high energy charged particle beams. Because of the simplified nature of the present apparatus, it may be incorporated into conventional electronic equipment requiring particle beams.

For a general description and illustration of the development of the beam traveling wave tube, reference is made to the publication Bell Laboratories Record of December 1946, and to the article therein, entitled The Beam Traveling Wave Tube by J. R. Pierce. In this reference the traveling wave tube is described as constituted of an electron gun similar to those employed in cathode ray tubes. An electron beam generated by the gun is directed along the axis of a long evacuated tube and impinged upon a collector anode. Within the tube, and surrounding the beam axis, is a closely wound wire helix which is excited at the electron gun end thereof by the weak signal to be amplified and which provides at the collector end thereof the amplified output signal. The tube contains no signal grids in the conventional sense.

Broadly speaking, the applied signal travels along the wire helix as an electromagnetic wave at a speed approaching the speed of light. As is determined by the pitch of the helix, the wave travels axially of the tube at a fraction of the speed of light; and the electron gun and collector anode potentials are arranged so that the average axial velocity of the electron beam through the helix is somewhat greater than the axial wave velocity.

Interaction of the electron beam and electromagnetic field components extending from the helix produces signal amplification. The greater the electron current and the longer the helix, the greater is the gain. In transit through the helix, the average electron Velocity is reduced, and the diminution of energy represented by this decreased velocity is imparted to the signal. The tube does not require a tuned circuit in the signal path, the wire helix being in effect an all-pass transmission line. Hence the tube is capable of operation over an exceedingly wide frequency range. In practice this range is limited somewhat by the impedance match of the helix to the external circuits.

In operation the signal appearing on the helix acts on the electron stream and gradually produces fluctuations in velocity and density. The

density modulated electron beam delivers ener y to the wave and over the helix section nearest the collector there is a substantially uniform gain per unit length of travel.

In my aforementioned co-pending patent applications there are described numerous embodiments of beam electromagnetic traveling wave tubes having application as broad band micro- Wave amplifiers, oscillators, frequency convertors or mixers and the like. The electron tubes disclosed in these above identified patent applications utilize wave guides for directing wave signals around the path of an electron beam. These guides permit direct coupling of the electromagnetic fields therein and the tube electron beam and have the advantage of precluding excessive energy radiation and undesirable coupling with external fields.

In the aforementioned patent applications it was demonstrated that signal amplification could be obtained in an electromagnetic traveling wave tube by causing an electron beam to traverse the axis of first and second, or input and output, helical wave guide sections of predetermined pitch and number of turns. The input wave guide was energized by the weak incoming signal, whereby the electron beam was bunched or density modulated. The modulated beam was then caused to traverse a second or output helical wave guide section and to deliver energy thereto to provide the amplified output signal.

In a tube of this construction, input and output wave guides are spaced axially of the electron beam. When certain conditions of beam velocity and helix structureare properly satisfied, considerable gain is obtained and the electron tubes are capable of either amplifier or oscillator operation; the latter being accomplished by coupling a predetermined portion of the output signal in the correct phase to the input wave guide. For traveling wave tubes having independent input and output wave guide sections, it has been determined that the optimum average beam velocity through the guides is equal to the axial component of velocity of the electromagnetic traveling wave.

It has also been demonstrated in the aforementioned patent applications that a single helical wave guide could be utilized for both modulating and extracting energy from an electron beam, such that an incoming signal could be coupled into the wave guide at the input or electron gun end thereof and the amplified output signal could be derived from the opposite end thereof. For single wave guide operation, it was demonstrated that optimum electron beam velocity was somewhat higher than the axial velocity component of the traveling wave inthe tube. In transit through the tube, each group of electrons was shown to deliver energy to the traveling wave, and the consequence thereof, the output signal, was at a level considerably above that introduced at the input'end of the guide.

It has been observed and clearly described in the above-mentioned co-pending patent applications that in transit through the beam traveling wave tube, the electron beam tends to become bunched in the positive potential regions of the traveling wave. In the traveling wave tube utilizing a single helical wave guide for amplification or signal generation and utilizing a beam velocity somewhat higher thanv thev traveling wave axial velocity, this bunching effect results in a general retardation of electrons in the beam. Physically, this retardation or general lowering of the average electron velocity in the beam is a consequence of the transfer of energy from the electron beam to the traveling electromagnetic wave. It is, in fact, this energy transfer from beam to wave whichresults in signal amplification such that the output traveling wave is at an energy level considerably above the input traveling wave.

If electrons were to enter the region of coupling with the electromagnetic traveling wave at an axial velocity somewhat less than the axial velocity of the, traveling wave, then this bunching eifect, which tends to synchronize the axial flow of electrons with the axial movement of positive potential regions of the traveling wave, would result in a general increase of average electron velocity. Obviously, this velocity increase which represents an increase in overall beam energy level is eifected by the extraction of energy from the traveling wave. For this reason, it was stated in co-pending application Serial No. 761,798 that electron velocities below the axial velocity of the traveling wave were undesirable since signal amplification could not be thus accomplished.

It is broadly an object of the present invention to provide means for utilizing the hereinabove mentioned principles of beam traveling wave tube operation for obtaining high intensity and high velocity charged particle beams readily adaptable for laboratory purposes and to inexpensive and non-hazardous commercial equipment. In its basic form the apparatus of this invention comprises an electron beam generator of a conveniently obtainable low energy level and associated means for providing an axially moving electromagnetic traveling wave arranged for interaction with the electron beam. At its input end the axial velocity component of the traveling wave is substantially equal to the axial velocity of the generated electron beam. However, means are provided for gradually and uniformly increasing the axial velocity compo nent of the traveling wave which correspondingly increases the average axial velocity of the electron beam at the expense of energy transferred from the traveling wave to the electron beam. There is thus produced an electron beam having an average velocity greaterthan that originally imparted thereto by the electron beam gener ating means.

The electromagnetic traveling wave having the necessary axial velocity component is obtained by suitably energizing a helical wave guide of the type completely described in the aforementioned co-pending patent applications. Gradual increase in axial velocity of this traveling wave while traversing its. path is efiected by forming the helical guide with uniformly increasing pitch in the direction of wave travel.

It is accordingly an object of the present invention to provide novel means for generating high intensity beams of electrostatically charged particles.

Another object of the present invention is to provide means incorporating guides for electromagnetic traveling waves for accelerating particles in a charged beam.

A further object of the present invention is to provide means for gradually increasing the axial component of velocity of a helically traveling electromagnetic wave.

Still another object of the present invention is out the use of impractically high voltages.

to provide means for accelerating electrons within a beam to velocities far in excess of those imparted by electrostatic fields in the beam generating means.

Another object of the present invention is to provide an electron beam accelerator utilizing a helical wave guide structure excited by a hi irequency electromagnetic wave.

A further object of the present invention is to provide a novel cathode ray tube utilizing a helical wave guide electron beam accelerator for obtaining high beam intensity without the requirement of externally generated and applied high direct voltage.

These and otherobjects of thepresent invention will now become apparent from the following detailed specification when taken in connection with the accompanying drawings in which:

Figure. l is an axial sectional view of a particle accelerator incorporating the principles of the present invention, and

Figure 2 is a sectional view of a cathode ray tube having beam accelerating means utilizing the novel particle accelerator illustrated in Figure 1.

With reference now to the drawings and more particularly to Figure 1 thereof, there is illustrated an electron beam accelerator tube incorporating the features of the present invention,

and comprising generally a comparatively large diameter, evacuated glass, or other dielectric cylinder I, having tapered ends l2 and |3.

Sealed into the left end |2 of the glass cylinder I i, are the electrodes of an electron gun 20 similar to those utilized in conventional cathode ray tube structures. As shown, the electron gun 20 comprises a heater 22 and its associated cathode 23, a centrally perforated control grid 24 and focusing and accelerating hollow cylindrical electrodes 25 and 26, respectively. When the electrodes comprising the electron gun 2B are energized from power ource I9 an axial beam of electrons of predetermined velocity is generated and directed along the axis 23 of cylinder II toward a disc shaped collector electrode 21 sealed into the right-hand end l3 of the tube, as viewed in Figure 1.

As is well understood in the electron gun art, the velocity of electrons leaving the accelerating electrode 26 is on the average substantially proportional to the square root of the potential difference between the cathode 23 and the accelerating electrode 26. As discussed hereinabove, this square root relationship between velocity and potential difference seriously limits the ability of conventional electron accelerating devices to provide extremely high velocity electrons with- In the present apparatus it will be understood that the electron gun 20 is of the type used in a conventional low-voltage cathode ray tube and consequently, does not by itself produce extremely high velocity electrons, nor require excessive hazardous voltages requiring particularly reliable safety enclosures and expensive and weighty insulation.

Structural means required for supporting the electron gun electrodes have been omitted from the drawing for clarity. Further description of the energizing means l9 are considered unnecessary at this point, since electron beam generators or electron guns of the type illustrated are suffi- 'ciently well-known in the electronic art.

In accordance with the broad principles of the present invention, the axial path of travel of the electron beam between the electron gun acceler ating electrode 26 and the collector electrode 21 is substantially enclosed within a helical wave guide assembly, a portion of which, as will be described below, serves to increase considerably the average velocity and energy level of the electron beam prior to its contact with collector electrode 21.

As illustrated in the drawing, the region within glass cylinder between accelerating electrode 26 and collector anode 21 is enclosed by a conductive metallic cylinder 3|, having an axis substantially coincident with the electron beam path 28 and lying in surface contacting relationship with the inner wall of glass cylinder The space within metallic cylinder 3| is divided'axially into two regions, the left portion 32 comprising a high frequency oscillator or exciter and the right portion 33 comprising an electron accelerator.

The exciter section 32 of the apparatus illustrated in Figure 1 comprises basically a beam traveling wave oscillator operating on the principles described in considerable detail in the aforementioned application Serial No. 788,724. This oscillator, as illustrated in Figure l, is constituted of a single helical wave guide 4|, formed of a thin, highly conductive metallic strip 42, helically wound in edgewise contacting relationship with the hollow cylindrical conductive enclosing cylinder 3|. It will be noted that the helical wave guide 4| is of substantially uniform pitch.

The radial dimension of the conductive strip 42, as illustrated in Figure 1, is somewhat less than the inner radius of the conductive cylinder 3| and accordingly, the inner edge 43 of the conductive strip 42 forms a helix lying in a cylindrical surface enclosing the axis 28 of electron travel.

The wave guide 4| defined by helically wound strip 42 and its enclosing conductive cylinder 3| is a helical passage of substantially uniform rectangular cross-section, and which progresses axially of the tube. Wave guide 4| is enclosed at any point by two adjacent turns of the conductive metallic strip 42 and by the metallic surface of enclosing cylinder 3|. The innermost wall of the helical wave guide 4|, lying between adjacent turns of helical edge 43, is open insofar as radiation of electromagnetic fields is concerned. Accordingly, there may be a transfer of energy between an electron beam traveling axlally through the tube and electromagnetic traveling waves progressing axially within the helical guide 4| within the exciter section 32 of the apparatus illustrated.

The end turns 45 and 46 of the conductive strip 42 are circular rather than helical and hence provide substantially planar terminations. As a consequence of this construction, the spaces between the last helical turns of strip 42 and the planar ends 45 and 46 uniformly diminish in cross section.

By means of lead 50, which connects the end turn 45 of strip 42 to the accelerating electrode 26, all metallic components within cylinder 3| are maintained at the static potential of anode 26.

In the aforementioned co-pending application Serial No. 788,724, it was clearly demonstrated that a beam traveling wave tube utilizing a single helical wave guide of substantially uniform pitch could be caused to oscillate by suitable feedback from output to input ends thereof. It was disclosed that one manner in which such feedback connection with the exciting section 32..

' structure-andthe average electron beam :velocity.

Since a. transfer of energy'is required from the electronxbeam ;to;;the-. traveling wave in .order. to v sustainzoscillation; the average :velocity of electrons will be somewhat lowered in their transit throughzthe exciting section 32 of the tube. illustrated in Figure; 1..

Self-oscillation. of this tube section may of course be accomplished by inserting suitable couplersextending t0*the input and output ends of thehelicalwave guidestructureshown, and .coupiling-1a portion ofthe output signal energy back to theinput end. This feedback'connection may include afrequency sensitive element such as a resonant cavity; in order that the excitingsection 32-ivoscillatev at a..fixed frequency. In the present illustration, the over-all structure issimplified by utilizing the principle of self-oscillation as aresult of mis-matched terminations.

A. suitable direct current component return pathxas requiredgby. theoscillator section 32 is assured by annular. conductive-insert 69 having reduced diameter opening. 10. formed. therein. Thisreduced section intercepts a portion of the electron stream, and by lead 50 these electrons are-returned. to the power. source, Thus, the number'of particles. passing through opening TB for-subsequent. acceleration is less than the total number of particles. in thebeamh The accelerating. region 33 ofthe electron tube illustratedin Figure- 1..is constituted essentially oi ar helical wave guide structure vin most respects similar to that previously described in Thus, as.- illustrated. in the drawing, the accelerating section 33 consists of..a. helical .wave guide 52 formed by a helically wound thin conductive strip 53.,(similar to strip 42) .extending from the planar end wall ABof the exciting section 32to the end of .theconductive cylinderfil adjacent the collector eelctrode21:. The helically woundstrip 53 in contact with conductive cylinder 3! defines'the helical waveguide passageifwhich progresses axially of the tube toward collector electrode 21 and which encloses the co-axial electron beam Path. 28;

The helical waveguide structure constituting the .accelerating'region 33 difiers from the-helical wave guide M which forms the oscillator section 32 in that the helical pitch of the metallic-strip 53 gradually increases in its progression toward collector electrode21. At its extremeleftturn 55 the; pitch of the accelerating section 33 is substantially equal to thepitch ofthehelical wave guide structure constituting the eXciter section 32': At'itsextreme right hand turn 56, the pitch of; the accelerating section 33' is considerably greater than the pitch at its input end 55.

In'order'to'preclude signal reflections from the right end of the accelerating waveguide .52, a uniformly tapered-helical dissipative block-:6 L is provided. withm-thelasti turn .of thelwave. guide.

52,formed by metallic strip 53.. The. block. 6.l is. preferably formed of a material capableoflef-i fectively dissipating microwave energy. Signal reflections from thev leftend of. the accelerating structure 33 have been observed. to besubstantially unimportant inefiect, and accordingly, this end of the accelerating structure 33 is merely,

abutted againstv the end turn. 46 of the exciter Wave guide structure...

The helical waveguidewithin the exciter region 32; and the .wave guide 52 within accelerating region 33 are electromagnetically coupled by a coupling element 65" extending through a perforation 66 in the abutting end walls of the helical strips. 42 and 531V The coupling element 65 is a short length of conductor formed to provide two loopsfi'l vandttwhichextend intothe final turn and the initial turn of the exciting and.accelerat'- mg helical Wave guides, respectively. In' this manner, high frequency wave energy which is generatedby the oscillator section 32.is coupled into the accelerating' section 33 for purposes. to be described in greater detail below.

In order to maintain electrons traversing axis 28 between accelerating electrode 26 and collector electrode 21 in. a sharply defined axial beam, means are providedfor establishing asubstantially uniform and unvarying axial magnetic field. As illustrated in Figure 1, thisisaccomplished by means of a multi-layersolenoid type coil 7!, coaxial with tube l and wound upon an insulating cylindrical coil formTIZ suitably secured over the outer surface of cylinder 1 I, and'extending axially over the region between the accelerating electrode 25 and the collector electrode21; Coil II is preferably energized'from a suitable direct current source (not shown in' the drawings). In accordance with well understood principles, an electron which tends to travel a path divergent from the axis 2801? the tube and hence angularly of the field established by thecoil H will beurged back to axis 28 as a consequence ofitsinteraction with the axial magnetic field.

The operation of the electron accelerator illustrated in'Figure I will now-be discussed-in detail, and it'will be' assumed-that allelectrodes are suitably energized, together with coil -71, and that exciter section 32 is operative as an oscillator developing high frequency wave energy.

Electrons entering the accelerating region 33 after axially. traversing :the oscillator section 32, willflhave an average axial velocity substantially equal to the axial'component of velocity of the high frequency traveling" wavegenerated within the excit'er-"section 32; As a result ofthe extraction of energy fromthe electron beam by thetraveling' wave 'withimth'eoscillator section 32, the average velocity ofelectrons entering the accelerating section'33 willbesomewhat less than the average velocity of electrons leaving the accelerating electrode 26'of the electron gun 20:

High frequency electromagnetic wave energy generatedin exciter' section 32 -and' coupledito the-helical accelerating wave guide 52::by means of coupling element 65 causes an electromagnetic wave to travel helically' within accelerating wave guide -52at substantiallythe speed'of light, toward the tapereddissipati'ng block. 6].. Evidently, the axial.component.;of..velocityt of. this last-mentionedtraveling wave at any point Within waveguide. .52 is 1 dependent upon thepitch of the helicalwave guide 52' at that point. As'previously. mentioned. the initiali pitch of. the .ac-

:aceleratingzawave aguide is preferably; substantially equal to the pitch of the exciter section wave guide 4| and accordingly, electrons entering the accelerating region 33 will be in substantial synchronism with the traveling wave axially progressing therethrough. In traversing the accelerating region 33, electron bunches within the beam remain synchronized with the axial progression of positive potential regions of the traveling wave electric fields extending inwardly toward the electron beam path. Although not thus illustrated, the accelerating wave guide 52 may be formed so that a number of turns thereof at the left end abutting the exciter section 32 are of a pitch equal to that of exciter wave guide 4|. This construction will be of aid in ensuring synchronism between the electron beam and traveling wave movements.

As a result of the uniform increase in pitch of the accelerating wave guide 33, the axial component of velocity of the traveling wave within the wave guide 52 gradually increases from the initial velocity at coupling loop 68. This progressive increase in axial wave velocity correspondingly progressively increases the axial velocity of the electron beam bunches synchronized with the movement of the traveling wave and as a consequence, the electrons emerging from the right-hand end of the accelerating region 33 have an average axial velocity considerably in excess of the velocity of these electrons as they entered the accelerating region 33. These high velocity electrons impinge upon collector electrode 21, in turn connected to a suitable load (not shown). Although the electrons emerging from the accelerating region 33 strike collectoranode 21 in bunches, a comparatively constant potential may be maintained at electrode 2! by means of a suitable load capacitor I5 connected between collector electrode 21 and a reference potential, such as ground.

The increase in energy represented by the increase in average electron velocity of course is derived from the traveling wave. Thus oscillator section 32 must be of sufiicient power to provide the required energy.

It will be noted that if electrons entering the accelerating region 33 are traveling axially at a speed approximately one-tenth that of light, and that if the pitch of the accelerating helical wave guide 52 is at its output end twice the pitch at its input end, then electrons will strike collector electrode 21 at a velocity approximately twotenths the velocity of light. From consideration of the aforementioned square root relationship between electron velocity and accelerating potential, it is apparent that doubling the electron velocity in the apparatus of Figure 1., corresponds to that velocity change which would be produced by an increase in potential of substantially four times that applied. Thus, by doubling the velocity of electrons in the accelerating region 33 of Figure 1, 10,000 volt electrons electrostatically accelerated may be further accelerated to a velocity corresponding to that ordinarily obtained by an accelerating potential of 40,000 volts. It will be noted, however, that 40,000 volts need not be applied to the structure to produce these electrons.

Clearly, the high intensity electrons obtained at the output of the accelerator, shown in Figure 1, need not be impinged upon a collector electrode. Instead, an X-ray anode may be substituted. or a test specimen for electron bombardment. These and other applications of high intensity beams are well known.

10 Although the electron tube of Figure 1 has been described as an accelerator incorporating a beam traveling wave exciting section, it is apparent that external excitation may instead be provided. Thus, an accelerator tube may be similarly constructed with the exception that the exciter region 32 is omitted and that coupling means (not shown) are provided for exciting the accelerating helical wave guide 52 with electromagnetic wave energy of suitable frequency and energy level. Also, one of the other known electron beam oscillator type electron tubes, as for example, the so-called McNally tube, may be substituted for the beam traveling Wave oscillator section 32.

The general application of a helical wave guide particle accelerator to a cathode ray tube structure having otherwise conventional characteristics is illustrated in Figure 2, and reference is now made thereto. The cathode ray tube I00 is in the conventional manner formed of a glass or other suitable evacuated envelope I01, having a flared portion, the face I02 of which is interiorly coated with a phosphor I03 of conventional composition. i

The neck I04 of the cathode ray tube I00 encloses a helical wave guide accelerating structure I05 which, in all respects, is identical to the metallic cylinder 3| and the enclosed helical guides illustrated in Figure 1. In view of this identity in structure, no further description of the features of accelerating system I05 is considered necessary at this point.

Also enclosed within the neck I04 of the oathode ray tube I00 is an electron gun 20 having the electrodes of the electron gun 20 of Figure 1.

The outer surface of the neck I04 of the oathode ray tube I00 is fitted with a coil form I2 housing a coil II (as in Figure l) which serves to maintain electrons generated by electron gun 20 in a narrow, axial beam I08 in their travel through the accelerating structure I05 within the tube neck.

For the cathode ray tube illustrated in Figure 2, the electron gun 20 may be of low-voltage design, although a high intensity spot H0 is desired upon the fluorescent screen I03. Acceleration of the electron beam to the desired high intensity level after leaving the electron gun 20 is accomplished by the helical wave guide accelerating system I05, operating in the manner already fully disclosed above in discussion of the apparatus illustrated in Figure 1. Due to the gradual increase in pitch of the accelerating wave guide within structure I05, electrons in beam I08 strike fluorescent screen I03 at a velocity far in excess of the velocity imparted thereto by electron gun 20. The need for impractically high potentials is thus obviated.

As the helical accelerating structure I05 contains a self-excited oscillator section, no high frequency signal need be coupled into the oatho oie ray tube from an external oscillation genera or.

An aquadag or other suitable conductive ring III is provided within the cathode ray tube in the region of the fluorescent screen I03. An external terminal H2 is provided for applying a suitable direct potential to this electrode. Magnetic deflection coils II5 are provided for the purpose of deflecting the electron beam I08 in a suitable manner in accordance with the usage of the tube.

Although the cathode ray tube electron beam accelerating means I05 has been illustrated in Figure -2-asidentical to that illustratedjinfil igure 1, it will be evident that various modifications may be made without in any manner altering the advantages obtained by use of high frequency helical wa-ve guide'accelerating means. For example, it is possible to excite the helical accelcrating section 105 from anexternal source of high-frequency-energy, and thus omit the exciting :section from thetube. This is economical of space within the cathode ray tube N10.

The electron accelerating system illustrated in Figure 1 may "be applied to various electronic apparatus otherthanthe cathode ray tube structure illustrated in Figure 2. .This particle accelerating*syst em,may be employed wherever .high velocity electrons are desired and wherever it is undesirable to "generate and. maintain. high direct potentials .required .for direct acceleration.

:The operating principles of this tubeneed not, of course, be confined tonegativeparticles (electrons) Rather, this .invention may be applied toaccelerate charged-particles of .any polarity. I Thus, sincezvarious:modifications-and extensions of the principles of the: present invention will nowxbecome' apparent-to those skilled in the art it ispreferredthat this-invention be limited not :by the 'zspecific embodiments herein illustrated anddescribed but by the spirit and scope io'fttheaappended claims.

.Icclaim:

:1. Arparticleacceleratorcomprising aiparticle gun for generatingaparticle beam, a helical wave guide,imeans fordirecting z'said particle beam axially :of said helical wave guide, means for coupling high frequency wave energy into said helical wave guide, -;said;.helical l wave guide having ."a -:pith providing an axial velocity of the traveling wave therein at successive coupling pointsrslightly:sreater than the velocity of the electron beam at corresponding coupling positions along the beam path :due to the axial velocity of the beam particles and beingofgpro- ,gressively Eincreasing pitch :in "the direction of particle movement in saidbeam.

12. An electron accelerator comprising, Within an evacuated envelope; an electron gun for generating an electronbeam, means for guiding said beamaxially of said envelope, a helically formed .conductive :member surrounding the path of said electron "beam, said member having a pitch to provide an axial velocity of the traveling wave from one point in the wave guide to a corresponding pointin the; next adjacent convolution ,of thewave guide Whichisslightly greater than the velocity of .theelectrons from a point; in the .beam .path:. adiacent -;to the afirst mentionedpoint .of the wave ,guide to a ,position in the :electron path adjacent to the--second:mentioned -point,in the waveguide and having a progressively increasing pitch over .a predeterminedaxialportion thereof, and 'means for introducing high .frequency-energy in"theiregion of said conductive strip.

3. An electron accelerator comprising, within an 1 evacuated envelope, an electron gun for generating an electron beam, said electron beam being directed axially-of said envelope, a cylin- .drical hollow-conductor co-axial with said -envelope, a conductive strip :helically formed .in edgewise-contactingrelationwith the inner surface .of said cylinder, the radial dimension of said strip being less than the inner radius of ,said cylinder, whereby .said cylinder and strip .de'finea helical .wave guide .progressing axially of said envelope andhaving an open inner wall,

. 1'2 the path of travel of said ,e'lectron'beam bein axial through saidhelical wave guide whereby an electromagnetic wave .fiowing within said guide is adapted for energy interchange with said electron beam, means for precluding wave reflections at the terminations of .saidhelical wave guide, said helical strip being formed with a gradually increasing pitch, the pitch at successive points providing an axial component of the-electromagnetic wave which is greater than the axial velocity of the adjacent electron beam in the direction of electron travel, and means'for energizing said helical Wave guide with high frequency energy.

4. An electron accelerator comprising, within an evacuated envelope, an .electrongun for generating .an electron beam, said electron beam being directed axially ,of saidenvelope, .a cylindrical hollow .conductor co-axial with said ,envelope, a conductive strip helically formedinedge wise contacting relation with the innersurface of said cylinder, the radial dimension of said strip being less than the inner radius of said cylinder, whereby said cylinder and strip define a helical wave guide progressing axially of said envelope and having an .open inner wall, the path of travel of said electron beambeingaxial through said helical wave guide whereby an electromagnetic wave flowing within said guide ,is adapted for energyinterchange with said electron beam, vmeans for precluding wave reflections at the terminations of said helical wave guide, said helical .strip being formed with a gradually increasing pitch, the pitch at successive points providing an axial component of the electromagnetic wave which .is greater than the axial velocity of the adjacentuelectron beam in the direction of electron travel, :andmeans for energizing said helical waveguide with high .frequency energy, said .last mentioned means comprising a high-frequencybeam traveling wave oscillator operative from said-electron beam and disposed axially between saidelectron gun and said helical wave guide.

'5. An electron accelerator comprising, within an evacuated envelope, an electron gunfor'generating an electron beam, said electron beam being "directed axially of said envelope, a cylindrical hollow conductor co-axial with said envelop-e, a conductive strip helically formed in edgewise'contacting relation with the inner surface of said cylinder, the radial dimensionof said strip being less than the inner radius of said cylinder, whereby :said cylinder and strip define a helical wave ,guide progressing axially .of said envelopeandhavingsan .openinner Wall, the path .of travel .of said electron beam being axial through said .helical wave guide whereby an electromagnetic wave flowing within said guide is adapted 'for energy interchange with said electron beam, means for precluding wave reflections at the terminations of said helical wave guide, said helical strip being formed with a gradually increasing pitch, the pitch at successive points providing an'axial'component of the electromagnetic wave which is greater than the axial velocity of the adjacent electron beam in the direction of electron travel, and means for energizing said helical wave guide with high frequency energy, said last mentioned means comprising a high frequency beam traveling waveoscillator operative from said electron beam and disposed axially between said electron gun and said helical wave guide, wave coupling means extending between said oscillator and said heli cal wave guide, and means between said oscillator and helical wave guide for intercepting a portion of said electron beam.

6. In an electrical discharge device, an electron emitter for generating a stream of electrons along an axial path of said discharge device, an accelerator for accelerating the electron stream, a collector electrode for receiving said electron stream, a first helical conductor encircling a first portion of said electron stream path, said conductor comprising a helical wave guide of thin highly conductive material, the helix being of a substantially uniform pitch and progressing axially of the electron path and in coupling relation therewith for effecting transfer of energy between an electron stream in said path and an electromagnetic travelling wave progressing axially within said helical guide, the pitch of said wave guide and the acceleration given the electrons in the electron stream providing an average velocity of the electrons in the electron path somewhat greater than the axial component of velocity of the electromagnetic traveling wave passing through the helical wave guide, the electron beam in said path exciting said wave guide to oscillate at a frequency which is determined by the physical configuration of the wave guide structure and the average electron beam velocity, a conductive strip terminating said wave guide and encircling said electron stream path and having an opening at its center which is of a smaller diameter than the diameter of said electron stream for intercepting a portion of said electron stream, an electrical connection from said wave guide to said accelerator for returning the intercepted electrons to said electron source, a second helical conductor axially juxtaposed with the first helical conductor and encircling a second portion of said electron stream path and comprising a helical wave guide of thin highly conductive material and progressing axially of said stream and in a coupling relation therewith and extending from the terminating strip of said first helical wave guide and toward the opposite end of said discharge device, the pitch of said wave guide being substantially equal to the pitch of the first helical wave guide and progressively increasing in pitch as it progresses toward the opposite end of said wave guide, a coupling element between said first and second wave guides for coupling said wave guides to each other to transfer the high frequency energy generated in said first wave guide to said second wave guide, the pitch of said second wave guide at its abutting position with said first wave guide and the speed of the electrons of reduced speed due to the transfer of energy from said electron stream to said first wave guide being such that the axial component of velocity of the traveling wave in said second wave guide is in substantial synchronism with the speed of the electrons in the path encircled by said second wave guide at the junction with said first wave guide, and the electron stream being accelerated by the axially accelerating wave traveling in said second wave guide to remain in synchronism with the axial progression of the traveling electromagnetic wave in said second wave guide, and a solenoid coil co-axial with said tube and secured thereto and extending axially from said accelerator electrode to said collector electrode and being energizable for sharply defining the axial beam.

'7. In an electrical discharge device, an electron emitter for generating a stream of electrons along an axial path of said discharge device, an accelerator for accelerating the electron stream, a collector electrode for receiving said electron stream, a first helical conductor encircling a first portion of said electron stream path, said conductor comprising a helical wave guide of thin highly conductive material, the helix being of a substantially uniform pitch and progressing axially of the electron path and in coupling relation therewith for effecting transfer of energy between an electron stream in said path and an electromagnetic traveling wave progressing axially within said helical guide, the pitch of said wave guide and the acceleration given the electrons in the electron stream providing an average velocity of the electrons in the electron path somewhat greater than the axial component of velocity of the electromagnetic traveling wave passing through the helical wave guide, the electron beam in said path exciting said wave guide to oscillate at a frequency which is determined by the physical configuration of the wave guide structure and the average electron beam velocity, a conductive strip terminating said wave guide and encircling said electron stream path and having an opening at its center which is of a smaller diameter than the diameter of said electron stream for intercepting a portion of said electron stream, an electrical connection from said wave guide to said accelerator for returning the intercepted electrons to said electron source, a second helical conductor axially juxtaposed with the first helical conductor and encircling a second portion of said electron stream path and comprising a helical wave guide of thin highly conductive material and progressing axially of said stream and in a coupling relation therewith and extending from the terminating strip of said first helical wave guide and toward the opposite end of said discharge device, the pitch of said wave guide being substantially equal to the pitch of the first helical wave guide and progressively increasing in pitch as it progresses toward the opposite end of said wave guide, a coupling element between said first and second wave guides for coupling said wave guides to each other to transfer the high frequency energy generated in said first wave guide to said second wave guide, the pitch of said second wave guide at its abutting position with said first wave guide and the speed of the electrons of reduced speed due to the transfer of energy from said electron stream to said first wave guide being such that the axial component of velocity of the traveling wave in said second wave guide is in substantial synchronism with the speed of the electrons in the path encircled by said second wave guide at the junction with said first wave guide, and the electron stream being accelerated by the axially accelerating wave traveling in said second wave guide to remain in synchronism with the axial progression of the traveling electromagnetic wave in said second wave guide.

8. In an electrical discharge device, an electron emitter for generating a stream of electrons along an axial path of said discharge device, an accelerator for accelerating the electron stream, a collector electrode for receiving said electron stream, a first helical conductor encircling said electron stream path and in coupling relation therewith, the helix being of a substantially uniform pitch and progressing axially of the electron pathand in coupling relation therewith for effecting transfer of energy vbetween-an :elec-tronstream in said ,path and an electromagnetic travelling wave progressing axially Within said helical guide, the pitch of said wave guide andthe acceleration-given the elecsaid streamand in a coupling relation therewith andextending from .theterminatinglstrip .of. said sfirstihelical wave guide and toward the opposite .end of said discharge device, the helical pitch of said. second wave guide gradually increasing as it progresses toward said opposite end of said discharge device, the pitch of said wave guide being substantially equal to the pitchof the first helical wave guide and progressively increasing in pitch as it progresses toward the opposite end ofsaid wave guide and a coupling element for coupling saidfirst and second wave guides to transfer the high .frequency energy generated in said first wave guide to said second wave guide, the pitch of saidsecond wave guide at its abutting position with said firs-t wave guide and the speed of the electrons of reduced speed due to the transfer of energy from said electron stream to said first Wave guide being suchthat the axial componentlof velocity of the travelling wave in said second wave guide is in substantial synchronism with the speed of the electrons in the path'encircled by said second wave guide at the junction with said first wave guide, and the electron stream beingaccelerated by the wave travel ling in saidsecond wave guide to remain in synchronism with the axial progression of the travelling electromagnetic wave in said second wave guide.

9. In an electrical discharge device, an electron emitter for generating a stream of electrons along an axialpath of said discharge device. an

accelerator fol-accelerating the electron stream,

a collector electrode for receiving said electron stream, and a helical conductor encircling said electron stream path and of thin highly conduc emitting end being such that the axial component of velocity of the travelling wave in said conductor is greater than the axial velocity of the electrons at the corresponding position, and the electron stream being accelerated by the wave travelling in said conductor to remain in syn- ..chronism with the axial progression of the travelling electromagnetic wave in said conductor.

10. In an electrical discharge device, an electron emitter for generating a stream of electrons along an axial path of said discharge-device, an accelerator for accelerating the electron stream,

-a collector electrode for receiving saidelectron stream, and ahelicalconductor encircling said electron'stream path and comprising a helical wave guide of thin highly conductive. material andprogressing axially .of said stream and in a coupling relation with said electron pathgthe helical pitch of said wave guide gradually increasing as it progresses along said axial path toward said collector electrode, the speed of the electrons in said electron stream and the pitch of said wave guide at the electron emitting end beingrsuch that the axial component of velocity of the travelling wave in said wave guide is greater than the axial velocity of the electrons at the corresponding position, and the electron stream being accelerated by the wave travelling in said wave guide to remain in synchronism with the axial progression of the travelling electromagnetic Wave in said wave guide.

11. In an electrical discharge device, an electron emitter for generating a stream of electrons along an axial path of said discharge device, an accelerator for accelerating'the electron stream, a collector electrode for receiving said electron stream, and a helical conductor encircling said electron stream path and comprising a helical Wave guide of thin highly conductive material and progressing axially of said stream and in a coupling relation with said electron path, the helical pitch of said Wave guide gradually increasing as it progresses along said axial path toward said collector electrode, the speed of the electrons in said electron stream and the pitch of said wave guide at the electron emitting end being such that the axial component of velocity of the travelling wave in said wave guide is greater than the axial velocity of the electrons at the corresponding position, and the electron stream being accelerated by the Wave travelling in said wave guide to remain in synchronism with the axial progression of the travelling electromagnetic wave in said wave guide, and a solenoid coil co-axial With said tube and secured thereto and extending axially from said accelerator electrode to said collector electrode and being energizable for sharply defining the axial beam.

12. In an electrical discharge device, an electron emitter for generating a stream of electrons along an axial path of said discharge device, a collector electrode for receiving said electron stream, and a helical conductor encircling said electron stream path and comprising a helical wave guide of thin highly conductive material and progressing axially of said stream and in a coupling relation with said electron path, the helical pitch of said conductor gradually increasing as it progresses along said axial path toward said collector electrode, the speed of the electrons in said electron stream and the pitch of said conductor at the electron emitting end being such that the axial component of velocity of the traveling Wave in said conductor is greater than the axial velocity of the electrons at the corresponding position, and the electron stream being accelerated by the wave traveling in said conductor to remain in synchronism with the axial progression of the traveling electro-magnetic Wave in said conductor.

13. In an electrical discharge device, an electron emitter ior generating a stream of electrons, a helical wave conductor adjacent said stream and in coupling relation thereto, said helical conductor having an increasing pitch in the direction in which said electrons move for acting on said electron stream to increase the electron velocity in accordance with the increasing pitch of said conductor, and the pitch of the wave conductor atany point being such that the axial velocity ofthe electromagnetic wave is greater than the 17 18 velocity of the electrons at the corresponding Number Name Date position. 2,367,295 Llewellyn Jan. 16, 1945 JOHN TILEY- 2,439,401 Smith Apr. 13, 1948 2,516,944 Barnett Aug. 1, 1950 REFERENCES CITED 5 2,575,383 Field Nov. 20, 1951 The following references are of record in the 2,578,434 Lindenblad Dec. 11, 1951 file of this patent: 2,584,802 Hansell Feb. 5, 1952 UNITED STATES PATENTS OTHER. REFERENCES Number Name Date 10 Article by Rudolf Kompfner, Reprint from 2,122,538 Potter July 5, 1938 Proc. in I. R. E. v01. 35, N0. 2, February 1947, pp. 2,233,126 Haeff Feb. 25, 1941 124-127,co'py in Div. 54.

2,300,052 Lindenblad Oct. 27, 1942 

